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United States Patent |
5,598,629
|
Schneider
,   et al.
|
February 4, 1997
|
Process for making contact with a silver contact base
Abstract
A contact includes a silver contact base, an intermediate silver layer and
a solder in the form of a platelet being provisionally fastened or tacked
to the intermediate silver layer prior to an actual soldering operation.
The silver contact base is soldered onto a contact carrier by the
intermediate silver layer and the solder platelet. A method for making a
contact includes pressing an intermediate silver layer onto a silver
contact base, then provisionally fastening or tacking a solder in the form
of a platelet to the intermediate silver layer and subsequently placing a
contact carrier on the solder platelet and soldering the contact carrier
to the solder platelet.
Inventors:
|
Schneider; Manfred (Lichtenfels, DE);
Clauss; Dietmar (Altenkunstadt, DE)
|
Assignee:
|
Siemens Aktiengesellschaft (Munich, DE)
|
Appl. No.:
|
254128 |
Filed:
|
June 6, 1994 |
Foreign Application Priority Data
| Dec 04, 1991[DE] | 41 39 998.6 |
Current U.S. Class: |
29/879; 29/267; 29/268; 200/268 |
Intern'l Class: |
H01R 043/20 |
Field of Search: |
200/268,267
29/874,876
|
References Cited
U.S. Patent Documents
2812406 | Nov., 1957 | Egan | 200/268.
|
3775067 | Nov., 1973 | Backstrom.
| |
4053728 | Oct., 1977 | Talento et al. | 200/267.
|
4138604 | Feb., 1979 | Harmsen et al.
| |
4342893 | Aug., 1982 | Wolf.
| |
5421084 | Jun., 1995 | Wolf et al. | 29/876.
|
Foreign Patent Documents |
0027893 | May., 1981 | EP.
| |
0283536 | Sep., 1988 | EP.
| |
0299099 | Jan., 1989 | EP.
| |
0301218 | Feb., 1989 | EP.
| |
2642338 | Feb., 1978 | DE.
| |
3107665 | Sep., 1982 | DE.
| |
3437981 | Aug., 1986 | DE.
| |
Primary Examiner: Arbes; Carl J.
Attorney, Agent or Firm: Lerner; Herbert L., Greenberg; Laurence A.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a Continuation of International Application Ser. No.
PCT/DE92/00998, filed Nov. 30, 1992.
Claims
We claim:
1. A method for making a contact, which comprises:
pressing an intermediate silver layer onto a silver contact base;
then provisionally fastening a solder in the form of a platelet to the
intermediate silver layer; and
subsequently placing a contact carrier on the solder platelet and soldering
the contact carrier to the solder platelet.
2. The method according to claim 1, which comprises carrying out the step
of the provisional fastening of the solder platelet by welding.
3. The method according to claim 1, which comprises carrying out the step
of the provisional fastening of the solder platelet by ultrasonic welding
to the intermediate silver layer.
4. The method according to claim 1, which comprises carrying out the step
of the provisional fastening of the solder platelet by gluing.
5. The method according to claim 3, which comprises pressing the solder
platelet onto the intermediate silver layer during the ultrasonic welding
with a pressure plate having small dotlike bumps.
6. The method according to claim 3, which comprises pressing the solder
platelet onto the intermediate silver layer during the ultrasonic welding
with a pressure plate having small, conical, dotlike bumps.
7. The method according to claim 5, which comprises vibrating the pressure
plate with ultrasonic vibrations being oriented at a tangent to a contact
surface of the solder platelet.
8. The method according to claim 6, which comprises vibrating the pressure
plate with ultrasonic vibrations being oriented at a tangent to a contact
surface of the solder platelet.
9. The method according to claim 1, which comprises pressing the solder
platelet flush into the intermediate silver layer prior to the soldering.
10. The method according to claim 1, which comprises inductively heating
the contact carrier, the solder platelet, the intermediate silver layer
and the silver contact base in the soldering operation.
11. The method according to claim 1, which comprises, in the pressing step,
selecting a silver contact base formed of a silver alloy and selecting an
intermediate layer formed of pure silver.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is a Continuation of International Application Ser. No.
PCT/DE92/00998, filed Nov. 30, 1992.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a contact with a silver contact base, which is
soldered to a contact carrier by means of a silver intermediate layer and
a solder. The invention also relates to a method for making the contact.
Among other uses, such contacts are used in relays and switches of the
most varied kinds.
The solders required for soldering are commercially available as flat
material. They already contain metered additives as soldering aids. It is
known for strips of contact solder and pure silver to be joined together
by hot rolling and for flat solder material then to be rolled as a third
layer onto the two-layer strip. The contacts are then cut from the
resultant three-layer strip and soldered onto the contact bearers or
carriers. It is a peculiarity of that production process that the rolled
edges have to be trimmed, so that waste is involved. Cutting apart the
contacts is also becoming increasingly problematic, if the contact
thicknesses are great.
It is also known to make two-layer contacts from a silver intermediate
layer which is cut to contact dimensions and from a press-on silver
contact base, and then to solder those contacts onto the respective
contact carrier by using a solder and soldering aids. With that mode of
operation no waste is produced, as long as strip material is used that
matches the width or length of the later contact at least in its width. In
larger quantities, however, that mode of operation is relatively
complicated, because exact positioning and metering of the solder and
soldering aid is required.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a contact with a
silver contact base and a process for making the same, which overcome the
hereinafore-mentioned disadvantages of the heretofore-known devices and
methods of this general type and which simplify the production of contacts
without impairing quality. In particular, the position of solder on an
intermediate silver layer of a two-layer contact should continue to be
reliably assured. Moreover, an upward creep of the solder on the silver
contact base upon soldering to a contact carrier should be prevented.
With the foregoing and other objects in view there is provided, in
accordance with the invention, a contact, comprising a silver contact
base; an intermediate silver layer; and a solder in the form of a platelet
being provisionally fastened or tacked to the intermediate silver layer
prior to an actual soldering operation; the silver contact base being
soldered onto a contact carrier by the intermediate silver layer and the
solder platelet.
As a result, the solder reliably stays positioned on the intermediate
silver layer without slipping or even dropping off prematurely, in other
words before the contact bearer or carrier is soldered on. This creates a
prerequisite for reliable manipulation of the parts to be soldered to one
another.
With the objects of the invention in view, there is also provided a method
for making a contact, which comprises pressing an intermediate silver
layer onto a silver contact base; then provisionally fastening or tacking
a solder in the form of a platelet to the intermediate silver layer; and
subsequently placing a contact carrier on the solder platelet and
soldering the contact carrier to the solder platelet.
This order in the production process assures reliable production of the
contacts in terms of both the position of the solder platelet and the
quality of the soldering operation. At the same time, it makes the
production process less expensive.
In accordance with another feature of the invention, prior to the
soldering, the solder platelet is located in an indentation in the
intermediate silver layer. As a result, in the soldering operation the
solder platelet is surrounded by this edge of the intermediate silver
layer resting on the contact carrier and cannot escape laterally as
easily. This indentation can be produced by a pressing or embossing step.
In accordance with a further feature of the invention, the tacking or
provisional fastening of the solder platelet is performed by welding.
Ultrasonic welding of the solder platelet to the intermediate silver layer
has proved to be especially advantageous, because it avoids heating of the
solder platelet. That could otherwise lessen the quality of the later
soldering.
In accordance with an added mode of the invention, the solder platelet is
pressed onto the intermediate silver layer during the ultrasonic welding
through a pressure plate with small dotlike bumps. This provision means
that the ultrasonic welding takes place only at the few pressure points of
the dotlike bumps, and can accordingly be carried out with very much less
exerted pressure and ultrasonic energy. This in turn means that the side
of the silver layer toward the solder layer has small indentations at the
those points where the dotlike bumps on the pressure plate were located.
In accordance with a concomitant mode of the invention, the solder platelet
is pressed flush into the intermediate silver layer prior to the
soldering. This creates the prerequisite for completely planar contact
with the contact carrier in the later soldering operation. At the same
time, because of the thus-produced lateral enclosure of the solder
platelet by the intermediate silver layer, lateral outflow of solder upon
soldering to the contact carrier is prevented, because the solder is bound
into the material of the edge of the intermediate silver layer. This also
prevents the solder material from creeping upward at the edges of the
silver during soldering. In the final analysis, this operation can replace
a separate operation of pre-embossing the intermediate silver layer.
Other features which are considered as characteristic for the invention are
set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a
contact with a silver contact base and a process for making the same, it
is nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and range
of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be best
understood from the following description of specific embodiments when
read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, diagrammatic, front-elevational view of a contact;
FIG. 2 is a side-elevational view of the two-layer contact;
FIG. 3 is a fragmentary, side-elevational view of the two-layer contact
after ultrasonic welding of the solder; and
FIG. 4 is a side-elevational view of the finished three-layer contact
before soldering onto the contact carrier.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the figures of the drawing in detail and first,
particularly, to FIG. 1 thereof, there is seen an exploded view which
shows the structure of a contact 1. The contact 1 includes a silver
contact base 2, an intermediate silver layer 4, a solder platelet 6 and a
contact bearer or carrier 8. The electrical contact silver or switch
silver contact base 2 in the exemplary embodiment is formed of a known
silver alloy. In the exemplary embodiment, the silver contact base 2 takes
the form of a rectangular plate having the dimensions of a later contact.
However, it could equally well take the form of a flat round disk or a
hemispherical dome. The intermediate silver layer 4, which can be seen in
FIG. 1 under the silver contact base 2, is adapted in its dimensions to
the outline of the silver contact base 2. In the exemplary embodiment, the
intermediate silver layer 4 is a pure silver. The solder platelet 6 can be
seen under the intermediate silver layer 4. The solder platelet is
essentially formed of copper and silver and in its commercially available
form it already contains all of the required soldering aids. The solder
platelet 6 has been cut from a strip of solder of the desired width, which
is available commercially. The contour of the solder platelet is adapted
to the contour of the intermediate silver layer 4, but the intermediate
silver layer protrudes past it on all sides by approximately 1 mm. The
contact carrier 8 for the contact 1 is shown in FIG. 1 under the solder
platelet 6. The contact carrier is formed of a flat material made of steel
that is surface-coated with copper.
In the making of the contact 1, the silver contact base 2 is first
compressed in a pressing tool with the intermediate silver layer 4 that is
cut to the contact size from flat silver material, to make a two-layer
contact seen in FIG. 2.
As is shown in FIG. 3, the solder platelet 6, which was previously cut from
a strip of flat solder material, is placed on the intermediate silver
layer 4 of this two-layer contact, it is positioned, and it is tacked or
provisionally fastened or welded by ultrasound using a sonotrode 10. The
sonotrode 10 has a contact surface facing toward the solder 6 and this
surface is provided with small bumps 12. In the exemplary embodiment, the
bumps are small pyramidlike points 12 that press the solder platelet 6
against the intermediate silver layer 4. When the piezoelectric ceramic is
activated, this pressure surface of the sonotrode 10 vibrates in the
direction parallel to the contact surface onto the solder 6. In the
process, surface elements of the solder platelet 6 that are located under
the conical bumps 12 on the contact surface of the sonotrode 10 and are
thus pressed to an increased extent against the intermediate silver layer
4, fuse with the intermediate silver layer, while the solder platelet
otherwise remains cold. Alternatively, it would also be possible to tack
or provisionally fasten the solder platelet to the intermediate silver
layer by gluing, through the use of an organic contact glue. This glue
then evaporates in the subsequent soldering operation.
The two-layer contact 2, 4 which is provided with the solder platelet 6 in
this way, is then placed underneath a pressing tool and pressed flat with
an exerted pressure of several tons per cm.sup.2. The solder platelet 6 is
thus pressed into the intermediate silver layer 4 as is seen in FIG. 4, so
that the intermediate silver layer surrounds the solder platelet on all
sides, except for the surface to be soldered later to the contact carrier
8. After the pressing operation, the two-layer contact is placed on the
contact carrier 8 and soldered to the contact carrier. To that end, the
contact carrier 8 together with the solder platelet 6, the intermediate
silver layer 4 and the silver contact base 2 is inductively heated to
approximately 750.degree. C. Due to the prior planar pressing, upon
soldering, the contact rests entirely flat on the contact carrier 8. As a
result, exactly reproducible, uniform conditions prevail over the entire
soldering surface. This is a prerequisite for automating the soldering
operation and for shortening the inductive heating time to approximately 1
second, without having to fear locally uncontrolled overheating. Moreover,
as a consequence of this planar pressing, the solder platelet is pressed
into the intermediate silver layer and enclosed on all sides, with the
exception of the contact surface, by the intermediate silver layer 4 on
the contact carrier 8. As a result, excess solder alloys to the silver
edge and is thus prevented from creeping laterally upward onto the silver
contact base.
It is a great advantage of this production process that the solder
platelets 6 can be positioned reliably on the intermediate silver layer 4
of the silver contact base, without having to be heated beforehand to a
temperature near the soldering temperature for that purpose. This avoids
the risk that heating of the solder might have disadvantages in later
soldering to the contact carrier 8. Moreover, manipulation of the parts is
simplified and made less expensive in this way.
Proof of the ultrasonic welding of the solder on the intermediate silver
layer can be provided by means of a micrograph.
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